Why "seven dog years" is a myth
The old "multiply by seven" rule is too simple because pets do not age at a steady pace. They mature very quickly in the first couple of years — a one-year-old dog is roughly a teenager — and then settle into a slower, steadier rate. Multiplying by a single constant overstates youth and understates old age.
This calculator follows the more realistic stepped model used by many vets: the first year counts as about 15 human years, the second adds roughly 9 more, and every year after that adds a smaller, species- and size-dependent amount.
Species and size
Cats and small dogs tend to live longer and age more gently in their later years, so each year beyond the second adds about four human-equivalent years. Medium and large dogs age faster late in life — large breeds add roughly six human years annually — which is why a big dog is considered "senior" earlier than a small one.
Pick the species, and for dogs the rough size band, so the later-year rate matches your pet as closely as a simple model can.
Treat it as a rough guide
This is an estimate, not a medical assessment. Real ageing depends on breed, genetics, diet, weight, dental health and veterinary care, and individual pets vary widely.
- Use the figure to gauge life stage (puppy/kitten, adult, senior), not as an exact human age.
- Mixed-breed and very large or very small dogs may age differently from the size bands here.
- Regular checkups matter more than any number; ask your vet about age-appropriate care.
- For health concerns, always consult a veterinarian rather than relying on a calculator.
Formula
first year = 15; second year = +9; each later year = +4 (cat) or +{small 4, medium 5, large 6} (dog)Frequently asked questions
- Why does dog size matter?
- Larger dogs tend to age faster in their later years, so each year beyond the second adds more human-equivalent years for large breeds than small ones.